A worker at the resort in Thap Sakae district of Prachuap Khiri Khan province, 280 kilometres (180 miles) south of Bangkok, found the badly beaten bodies of Michael Raymond, 68 and Suchada Baokhamdee, 52, Tuesday afternoon in their beach front bungalow.
"They were beaten with a chair and other hard objects," case officer Captain Winai Raila-aied told AFP by telephone.
Police have arrested three Thai men, including two resort staff and a villager, who all confessed to robbery and murder.
"At first two suspects -- a chef and a security guard -- admitted they had robbed the couple of 2,000 baht ($67), a mobile phone and a Bangkok Bank ATM card," Winai said. "Now all three have confessed to their wrongdoing," he said.
The couple had checked in at the resort on the Gulf of Thailand a day earlier.
Winai said Raymond had lived in the northeastern Thai province of Khon Kean for two years since he got married.